If you want to get I2s from your Oppo you need to get an I2s board from Oppomod.comĀ https://www.oppomod.com/index.html
The Chinese black box will only separate audio from video afaik, no I2s.
There is no cable standard for I2s at present so either stick with the same manufacturer or get Chinese cables that allow you to swap conductors, but their SQ maybe not so good.